The present invention relates to a reference electrode of the type used in testing or measuring various samples, such as serum or a blood sample.
More particularly, the present invention relates to such a reference electrode of the type including an internal electrode provided within a chamber within a cylindrical holder, the chamber being filled with a reference fluid which is connected to the exterior of the reference electrode by means of a liquid junction at the lower end thereof.
Reference electrodes of the above general type are known and have generally employed liquid junctions of the so-called sleeve type, pinhole type or ceramic type. All of these prior art types of liquid junctions however have suffered from certain inherent disadvantages.
Liquid junctions of the sleeve type are normally formed of an inner tube portion having therein a penetrating hole and an outer tube portion or sleeve which is attached to the outer peripheral surface of the inner tube by mutual friction. This type of liquid junction is disadvantageous in that a considerable amount of inner fluid or liquor leaks therefrom, and in that it is virtually impossible to manufacture this type of liquid junction of a very small size, whereby the device cannot be employed for the measurement of a small amount of a sample.
Liquid junctions of the pinhole type include a member having a small hole therein. This type of liquid junction however, is disadvantageous in that such pinhole is readily susceptible to being filled up with foreign solid substances from the exterior. Thus, this type of liquid junction cannot be employed for the measurement of a sample solution containing organic or other foreign substances having a tendency to deposit.
Furthermore, liquid junctions formed of a ceramic material are also very easily filled up with foreign solid matter such as organic polymeric substances, particularly protein substances when the electrode is used for the measurement of blood or serum. Also, liquid junctions of the ceramic type allow a considerable leakage of the inner liquor, thereby making it necessary to frequently supplement the supply of liquor to the inner chamber of the reference electrode. Thus, a reference electrode including a liquid junction of the ceramic type normally includes a rubber stopper which must be removed to replenish the supply of inner liquor. This type of operation however may easily result in spilling of the inner liquor. For the above reasons, reference electrodes employing liquid junctions of the ceramic type are quite disadvantageous from the standpoint of handling and are also uneconomical.